In the fabric printing industry, fabrics are typically colored with coloring agents, such as dyes or pigments, using a screen printing technology. Most large-scale fabric printing operations employ rotary screen printing technologies that utilize patterns incorporated into fine metal screens that are shaped into cylindrical forms. The coloring agents, are often in a fluid paste form, are pumped through dedicated tubing into the interior of fine cylindrical metal screens and are subsequently transferred to the fabric through the patterned pathways in the fine metal screens by a squeegee that presses the paste through the screens and onto the fabric. After each screen print run, with each color way (i.e., a color variant of the same pattern that uses different color combination), the rotary screen printer must be shut down to clean the various color pastes from the tubing and screens. This cleanup process is time intensive and environmentally unfriendly because it produces a large amount of effluent stream during the cleanup process. In addition to cleaning the rotary screen printer, a different screen must be inserted, aligned and adjusted into the printer to print a different pattern on the fabric.
To ensure that the pattern printed on the fabric is not distorted, industrial fabric printing machines stretch the fabric, and subsequently glue the stretched fabric to a belt that is run through the printing machine. The moving belt is indexed through the printing machine and the various screen stages. By attaching the fabric to the belt, the fabric is prohibited from moving with respect to the belt, which ensures fabric motion control that helps guarantee adequate registration of the fabric through the various stages in such a way that the fabric moves in a path corresponding to the movement path of the belt. However, gluing the fabric to the belt is an extremely dirty process that creates a significant environmentally unfriendly waste stream resulting from the gluing process and the subsequent washing and stripping processes. These inherent problems make industrial fabric printing processes prohibitive for use by smaller-scale users in the short run or sample printing situations. Furthermore the need for short and sample quantity runs generally exists in an office or a store setting, which generally is not designed to handle, treat and dispose of industrial waste streams.
To remedy the need for printing processes available on a smaller than industrial scale, digital ink-jet printing processes on fabrics have been developed. As known to those of ordinary skill in the art, digital printers utilize minute droplets of ink colorant that are ejected from nozzles of the ink-jet printer onto a target surface, such as, paper or fabric. In order to produce an image or pattern with the desired print quality on the fabric, special pre and post-treatment processes are employed. Pre & Post printing processes are used to deposit an ink receptive layer, and then to condition the fabric and the ink receptive layer for optimal print quality condition. Finally, the colorants require a fixing process (post processing) that either physically or chemically fix the colorants to the fabric fibers. The pre-printing conditioning steps are used to initially control the humidity and temperature of the fabric to provide an optional ink reception state for the fabric, and the post-processing steps are used to “fix” the ink colorant to the fabric, after the ink colorant has been received by the fibers in the fabric. In addition, pre-treating the fabric with organic materials increases ink receptivity and reduces the amount of ink spread, which arises from bleeding of the printed ink along the fibers in the fabric. The ink colorant is generally prevented from “blowing through” in digital printing systems by laminating the fabric with a paper-backing layer. This produces a barrier to the ink “blow through.” The paper layer also stabilizes the fabric for feeding through a traditional ink-jet printer media path.
Backed fabrics may be passed through some modified ink-jet printers for the printing of a pattern on the backed fabric. However, the use of off-line paper backings may be costly, time consuming, and may limit the range of fabrics that may be fed through the ink-jet printer. Furthermore, the fabric may be damaged when the fabric is removed from the paper backing. Thus, printing on unbacked fabrics is often desirable.
As known to those of ordinary skill in the art, the problems of printing on unbacked fabrics using an ink-jet printer are not trivial. The fundamental nature of woven fabrics makes feeding the unbacked fabric and printing a pattern on the unbacked fabric more complex than traditional ink-jet printing on paper. For instance, fabrics have an almost infinite variation in fabric characteristics due to various factors including, but not limited to, the type of fiber used in the fabric, the fiber weight, the fabric weight, the different blends of materials used in the fiber, the weave pattern used to create the fabric, the environmental conditions existing at the time of printing, the pre-treatments used on the fabric, the surface finish of the fabric, the varying moisture contents of the fiber in the fabric, the non-linear behavior of woven materials, and the difference in fabric behavior between wet and dry fabrics. These factors prohibit the unbacked fabrics from moving accurately and uniformly through the printing processes using standard media-moving machines used in the traditional ink-jet printers.
The challenge is to make a clean, versatile and user-friendly, unbacked printing system for non-mill applications for producing printed fabrics in the short run and sampling quantities. An inkjet textile printing system that addresses the issues of tension control, closed-loop displacement control, fabric conditioning, and fabric motion control using an unbacked fabric transfer system would be desirable. A digital ink-jet textile printing system that produces printed patterns consistently, with a low level of distortion, and yet is practical for use in the short-run and sampling industries, would likewise be desirable. Of course, improvements to a printing system that allow the ink-jet printer to print a pattern with a low level of distortion on the unbacked fabric would also have utility in industrial screen printing processes, especially for proofing, color matching, and precise pattern replication needs.